Topic Overview

🔶 LEGIONELLA, BARTONELLA & UNUSUAL BACTERIA

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🔹 LEGIONELLA PNEUMOPHILA

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🔸 Morphology

• Gram-negative thin bacilli

• Poorly stained with Gram stain (silver stain better)

• Non-sporing

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🔸 Transmission (VERY HIGH-YIELD)

• Aerosol inhalation

• Sources:

  • Air-conditioning systems

  • Cooling towers

  • Water systems

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🔸 Culture

• BCYE agar (Buffered Charcoal Yeast Extract)

• Requires:

  • Cysteine

  • Iron

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🔸 Intracellular Survival

• Survives in macrophages

• Inhibits phagosome–lysosome fusion

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🔸 Pathogenesis

Inhalation
↓
Entry into lungs
↓
Phagocytosis by macrophages
↓
Intracellular multiplication
↓
Cell lysis
↓
Inflammation
↓
Pneumonia

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🔸 Clinical Features (Legionnaires’ Disease)

• High fever

• Cough

• Dyspnea

• Atypical pneumonia

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🔸 Diagnosis (VERY HIGH-YIELD)

• Urinary antigen test (rapid, most useful)

• Culture (BCYE agar)

• PCR

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🔬 SLIDES (EXAM FAVORITE)

Legionella on BCYE agar

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🔹 BARTONELLA

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🔸 Bartonella henselae

• Causes Cat scratch disease

Transmission

• Cat scratch / bite

Clinical Features

• Regional lymphadenopathy

• Fever

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🔸 Bartonella quintana

• Causes Trench fever

Transmission

• Body louse

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🔸 Special Feature (VERY HIGH-YIELD)

• Angiogenesis → Bacillary angiomatosis

  • Seen in immunocompromised

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🔬 SLIDES (EXAM FAVORITE)

Bartonella histology

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🔹 STREPTOBACILLUS MONILIFORMIS

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🔸 Disease

• Rat bite fever

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🔸 Transmission

• Rat bite

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🔸 Clinical Features

• Fever

• Rash

• Arthritis

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🔹 WHIPPLE DISEASE

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🔸 Organism

• Tropheryma whipplei

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🔸 Pathogenesis

Infection
↓
Macrophage infiltration
↓
Malabsorption

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🔸 Key Feature (VERY HIGH-YIELD)

• PAS-positive macrophages

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🔬 SLIDES (EXAM FAVORITE)

PAS stain (Whipple disease)

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📊 TABLES (VERY HIGH-YIELD)

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🔸 Legionella vs Typical Pneumonia

Feature	Legionella	Typical (e.g., Pneumococcus)
Transmission	Aerosol	Droplet
Staining	Poor Gram stain	Good Gram stain
Growth	BCYE agar	Blood agar
Intracellular	Yes	No

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🔸 Bartonella Species Comparison

Species	Disease	Transmission
B. henselae	Cat scratch disease	Cat
B. quintana	Trench fever	Louse

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🔸 Zoonotic Infections

Organism	Source	Disease
Bartonella	Cat	Cat scratch disease
Streptobacillus	Rat	Rat bite fever
Pasteurella	Animal bite	Cellulitis
Yersinia pestis	Flea	Plague

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🔸 Unusual Bacteria Summary

Organism	Disease
Legionella	Pneumonia
Bartonella	Cat scratch disease
Streptobacillus	Rat bite fever
Tropheryma	Whipple disease

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🧠 DIAGRAMS / FLOWCHARTS

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🔹 Legionella Intracellular Survival

Inhalation
↓
Macrophage uptake
↓
Inhibits phagolysosome fusion
↓
Intracellular multiplication
↓
Cell lysis
↓
Pneumonia

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🔹 Cat Scratch Disease Pathway

Cat scratch
↓
Bacterial entry
↓
Local infection
↓
Lymph node involvement
↓
Lymphadenopathy

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🔹 Zoonotic Transmission

Animal/vector
↓
Human exposure
↓
Entry into body
↓
Infection

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🔥 HIGH-YIELD POINTS

• Legionella → intracellular + BCYE agar

• Urinary antigen → best diagnostic test

• Bartonella → angiogenesis (bacillary angiomatosis)

• Rat bite fever → Streptobacillus

• Whipple disease → PAS-positive macrophages